import {
    LoadingManager
} from 'three';
import { CompressedTextureLoader } from './compressed_texture_loader';

/**
 * for description see https://www.khronos.org/opengles/sdk/tools/KTX/
 * for file layout see https://www.khronos.org/opengles/sdk/tools/KTX/file_format_spec/
 *
 * ported from https://github.com/BabylonJS/Babylon.js/blob/master/src/Misc/khronosTextureContainer.ts
 */


export class KTXLoader extends CompressedTextureLoader {

    public constructor (manager?: LoadingManager) {

        super(manager);

    }

    public parse (buffer: ArrayBuffer, loadMipmaps?: boolean) {

        const ktx = new KhronosTextureContainer(buffer, 1);

        return {
            mipmaps: ktx.mipmaps(loadMipmaps),
            width: ktx.pixelWidth,
            height: ktx.pixelHeight,
            format: ktx.glInternalFormat,
            isCubemap: ktx.numberOfFaces === 6,
            mipmapCount: ktx.numberOfMipmapLevels
        };

    }

}


const HEADER_LEN = 12 + (13 * 4); // identifier + header elements (not including key value meta-data pairs)
// load types
const COMPRESSED_2D = 0; // uses a gl.compressedTexImage2D()
//const COMPRESSED_3D = 1; // uses a gl.compressedTexImage3D()
//const TEX_2D = 2; // uses a gl.texImage2D()
//const TEX_3D = 3; // uses a gl.texImage3D()

class KhronosTextureContainer {

    public readonly arrayBuffer: ArrayBuffer;

    public glType: number;
    public glTypeSize: number;
    public glFormat: number;
    public glInternalFormat: number;
    public glBaseInternalFormat: number;
    public pixelWidth: number;
    public pixelHeight: number;
    public pixelDepth: number;
    public numberOfArrayElements: number;
    public numberOfFaces: number;
    public numberOfMipmapLevels: number;
    public bytesOfKeyValueData: number;

    public loadType: number;

    /**
     * @param {ArrayBuffer} arrayBuffer- contents of the KTX container file
     * @param {number} facesExpected- should be either 1 or 6, based whether a cube texture or or
     * @param {boolean} threeDExpected- provision for indicating that data should be a 3D texture, not implemented
     * @param {boolean} textureArrayExpected- provision for indicating that data should be a texture array, not implemented
     */
    public constructor (arrayBuffer: ArrayBuffer, facesExpected /*, threeDExpected, textureArrayExpected */) {

        this.arrayBuffer = arrayBuffer;

        // Test that it is a ktx formatted file, based on the first 12 bytes, character representation is:
        // '´', 'K', 'T', 'X', ' ', '1', '1', 'ª', '\r', '\n', '\x1A', '\n'
        // 0xAB, 0x4B, 0x54, 0x58, 0x20, 0x31, 0x31, 0xBB, 0x0D, 0x0A, 0x1A, 0x0A
        const identifier = new Uint8Array(this.arrayBuffer, 0, 12);
        if (identifier[0] !== 0xAB ||
            identifier[1] !== 0x4B ||
            identifier[2] !== 0x54 ||
            identifier[3] !== 0x58 ||
            identifier[4] !== 0x20 ||
            identifier[5] !== 0x31 ||
            identifier[6] !== 0x31 ||
            identifier[7] !== 0xBB ||
            identifier[8] !== 0x0D ||
            identifier[9] !== 0x0A ||
            identifier[10] !== 0x1A ||
            identifier[11] !== 0x0A) {

            console.error('texture missing KTX identifier');
            return;

        }

        // load the reset of the header in native 32 bit uint
        const dataSize = Uint32Array.BYTES_PER_ELEMENT;
        const headerDataView = new DataView(this.arrayBuffer, 12, 13 * dataSize);
        const endianness = headerDataView.getUint32(0, true);
        const littleEndian = endianness === 0x04030201;

        this.glType = headerDataView.getUint32(1 * dataSize, littleEndian); // must be 0 for compressed textures
        this.glTypeSize = headerDataView.getUint32(2 * dataSize, littleEndian); // must be 1 for compressed textures
        this.glFormat = headerDataView.getUint32(3 * dataSize, littleEndian); // must be 0 for compressed textures
        this.glInternalFormat = headerDataView.getUint32(4 * dataSize, littleEndian); // the value of arg passed to gl.compressedTexImage2D(,,x,,,,)
        this.glBaseInternalFormat = headerDataView.getUint32(5 * dataSize, littleEndian); // specify GL_RGB, GL_RGBA, GL_ALPHA, etc (un-compressed only)
        this.pixelWidth = headerDataView.getUint32(6 * dataSize, littleEndian); // level 0 value of arg passed to gl.compressedTexImage2D(,,,x,,,)
        this.pixelHeight = headerDataView.getUint32(7 * dataSize, littleEndian); // level 0 value of arg passed to gl.compressedTexImage2D(,,,,x,,)
        this.pixelDepth = headerDataView.getUint32(8 * dataSize, littleEndian); // level 0 value of arg passed to gl.compressedTexImage3D(,,,,,x,,)
        this.numberOfArrayElements = headerDataView.getUint32(9 * dataSize, littleEndian); // used for texture arrays
        this.numberOfFaces = headerDataView.getUint32(10 * dataSize, littleEndian); // used for cubemap textures, should either be 1 or 6
        this.numberOfMipmapLevels = headerDataView.getUint32(11 * dataSize, littleEndian); // number of levels; disregard possibility of 0 for compressed textures
        this.bytesOfKeyValueData = headerDataView.getUint32(12 * dataSize, littleEndian); // the amount of space after the header for meta-data

        // Make sure we have a compressed type.  Not only reduces work, but probably better to let dev know they are not compressing.
        if (this.glType !== 0) {

            console.warn('only compressed formats currently supported');
            return;

        } else {

            // value of zero is an indication to generate mipmaps @ runtime.  Not usually allowed for compressed, so disregard.
            this.numberOfMipmapLevels = Math.max(1, this.numberOfMipmapLevels);

        }

        if (this.pixelHeight === 0 || this.pixelDepth !== 0) {

            console.warn('only 2D textures currently supported');
            return;

        }

        if (this.numberOfArrayElements !== 0) {

            console.warn('texture arrays not currently supported');
            return;

        }

        if (this.numberOfFaces !== facesExpected) {

            console.warn('number of faces expected' + facesExpected + ', but found ' + this.numberOfFaces);
            return;

        }

        // we now have a completely validated file, so could use existence of loadType as success
        // would need to make this more elaborate & adjust checks above to support more than one load type
        this.loadType = COMPRESSED_2D;

    }

    public mipmaps (loadMipmaps?: boolean): { data: Uint8Array, width: number, height: number }[] {

        const mipmaps = [];

        // initialize width & height for level 1
        let dataOffset = HEADER_LEN + this.bytesOfKeyValueData;
        let width = this.pixelWidth;
        let height = this.pixelHeight;
        const mipmapCount = loadMipmaps ? this.numberOfMipmapLevels : 1;

        for (let level = 0; level < mipmapCount; level++) {

            const imageSize = new Int32Array(this.arrayBuffer, dataOffset, 1)[0]; // size per face, since not supporting array cubemaps
            dataOffset += 4; // size of the image + 4 for the imageSize field

            for (let face = 0; face < this.numberOfFaces; face++) {

                const byteArray = new Uint8Array(this.arrayBuffer, dataOffset, imageSize);

                mipmaps.push({ 'data': byteArray, 'width': width, 'height': height });

                dataOffset += imageSize;
                dataOffset += 3 - ((imageSize + 3) % 4); // add padding for odd sized image

            }

            width = Math.max(1.0, width * 0.5);
            height = Math.max(1.0, height * 0.5);

        }

        return mipmaps;

    }

}